Fermentation products: poly-3-hydroxybutyrate (PHB)

The biopolymer poly-3-hydroxybutyrate (PHB) is a polyester produced by certain bacteria processing glucose, corn starch or wastewater. Its characteristics are similar to those of the petroplastic polypropylene. PHB production is increasing. The South American sugar industry, for example, has decided to expand PHB production to an industrial scale. PHB is distinguished primarily by its physical characteristics. It can be processed into a transparent film with a melting point higher than 130 degrees Celsius, and is biodegradable without residue.

Properties of poly-3-hydroxybutyrate (PHB)

• Water insoluble and relatively resistant to hydrolytic degradation. This differentiates PHB from most other currently available biodegradable plastics, which are either water soluble or moisture sensitive.
• Good oxygen permeability.
• Good ultra-violet resistance but poor resistance to acids and bases.
• Soluble in chloroform and other chlorinated hydrocarbons.
• Biocompatible and hence is suitable for medical applications.
• Melting point 175°C., and glass transition temperature 2°C.
• Tensile strength 40 MPa, close to that of polypropylene.
• Sinks in water (while polypropylene floats), facilitating its anaerobic biodegradation in sediments.
• Nontoxic.
• Less ‘sticky’ when melted, making it a potentially good material for clothing in the future.